measurement of ocean currents

Currents also can be measured by drifting
floats, either at the surface or at a given depth. Tracking the location of the
floats is critical. Surface
floats can be followed by satellite, but subsurface drifters must be tracked acoustically. A drifter of this sort acts as an acoustical source and transmits signals that can be followed by a ship with hydrophones suspended into the sea. For such...